The present invention relates generally to electronic control of an internal combustion engine having first and second groups of cylinders. In particular, this invention relates to a system and method of controlling the air/fuel ratio in the second group of cylinders based on a feedback signal received from an oxygen exhaust sensor located downstream of the second group of cylinders and a feedback signal from at least one exhaust gas oxygen sensor located downstream of the first group of cylinders.
To meet current emission regulations, automotive vehicles can regulate the air/fuel ratio (A/F) supplied to the vehicles"" cylinders so as to achieve maximum efficiency of the vehicles"" catalysts. For this purpose, it is known to control the air/fuel ratio of internal combustion engines using an exhaust gas oxygen (EGO) sensor positioned in the exhaust stream from the engine. The EGO sensor provides feedback data to an electronic controller that calculates preferred A/F values over time to achieve optimum efficiency of a catalyst in the exhaust system. It is also known to have systems with two EGO sensors in the exhaust stream in an effort to achieve more precise A/F control with respect to the catalyst window. Normally, a pre-catalyst EGO sensor is positioned upstream of the catalyst and a post-catalyst EGO sensor is positioned downstream of the catalyst. Finally, in connection with engines having two groups of cylinders, it is known to have a two-bank exhaust system coupled thereto where each exhaust bank has a catalyst as well as pre-catalyst and post-catalyst EGO sensors. Each of the exhaust banks corresponds to a group of cylinders in the engine. The feedback signals received from the EGO sensors are used to calculate the desired A/F values in their respective group of cylinders at any given time. The controller uses these desired A/F values to control the amount of liquid fuel that is injected into the cylinders by the vehicle""s fuel injector. It is a known methodology to use the EGO sensor feedback signals to calculate desired A/F values that collectively, when viewed against time, form A/F waveforms having ramp portions, jumpback portions and hold portions, as shown in FIG. 4.
Sometimes, in a two-bank, four-EGO sensor exhaust system, one of the pre-catalyst EGO sensors degrades. In other circumstances, it is desirable to purposely eliminate one of the pre-catalyst EGO sensors in a two-bank system to reduce the cost of the system. In either event, it is desirable to be able to control the A/F in the group of cylinders coupled to the exhaust bank having only one operational EGO sensor by using the feedback signals received from the three operational EGO sensors alone. It is a known methodology to compensate for a degraded or missing pre-catalyst EGO sensor in one of the exhaust banks by having the A/F values in the corresponding group of cylinders mirror the A/F values in the other group of cylinders. Essentially, this known methodology simply calculates desired A/F values over time for the group of cylinders coupled to two properly functioning EGO sensors and uses those A/F values for both banks. But this methodology fails to utilize the feedback signal provided by the post-catalyst EGO sensor in the exhaust bank having the degraded or missing pre-catalyst EGO sensor. Therefore, the A/F values applied to the group of cylinders coupled to the degraded or missing pre-catalyst EGO sensor do not benefit from any feedback signal specific to that bank, and, as a result, the A/F values used in that group of cylinders may not be optimal to enable the corresponding catalyst to perform most efficiently.
Finally, in certain applications it is desirable for the A/F waveform created by the calculated A/F values of one of the banks to be inverted relative to the A/F waveform of the other bank. The inversion of the A/F waveform in one of the banks relative to the A/F waveform in the other bank improves operation of the system in certain cases, such as when the engine is in idle mode.
Therefore, it is desirable to have an improved methodology and system for calculating A/F values for a group of cylinders coupled to an exhaust bank having a degraded or missing pre-catalyst EGO sensor. The improved methodology and system should utilize the feedback signal received from the post-catalyst EGO sensor in the exhaust bank having the degraded or missing pre-catalyst EGO sensor to calculate more responsive A/F values and thus enable the catalyst to operate more efficiently.
The present invention is directed toward a new methodology and system for controlling the A/F level in one of two groups of cylinders in an internal combustion engine by using a feedback signal from an EGO sensor coupled downstream of that group of cylinders and a feedback signal from at least one EGO sensor coupled downstream of the other group of cylinders. In an engine having two groups of cylinders coupled to a two-bank exhaust system, the present invention calculates preferred A/F values for the second group of cylinders based on feedback signals received from a pre-catalyst EGO sensor and a post-catalyst EGO sensor coupled to the first group of cylinders and a feedback signal received from a post-catalyst EGO sensor coupled to the second group of cylinders. The present invention is particularly applicable to well-known two-bank four EGO sensor exhaust systems where one of the pre-catalyst EGO sensors degrades or is purposefully omitted from the system.
Specifically, a controller in the present invention uses well-known methodologies to generate preferred A/F values for the group of cylinders coupled to two functioning EGO sensors (the xe2x80x9cFirst Bankxe2x80x9d). The controller, in cooperation with a fuel injector, uses those A/F values to control the amount of liquid fuel that is injected into those cylinders, according to well-known methods. The preferred A/F values form an A/F waveform over time, which includes ramp portions, jumpback portions and hold portions, as is known in the art. This invention can also be used in connection with a variety of different A/F waveforms. The controller uses a feedback signal provided by the post-catalyst EGO sensor of the exhaust bank coupled to one operational EGO sensor (the xe2x80x9cSecond Bankxe2x80x9d) to modify the A/F values calculated for the First Bank, thereby generating A/F values for the Second Bank. According to one preferred embodiment of this invention, the A/F values for the Second Bank are calculated by adding a certain offset value to the corresponding A/F values of the First Bank. The offset value for each A/F value of the Second Bank is calculated based on the feedback signal from the post-catalyst EGO sensor in the Second Bank.
In a second embodiment of this invention, the controller generates an A/F waveform for the Second Bank that is inverted relative to the A/F waveform for the First Bank. First, A/F values for the Second Bank are calculated by adding a certain offset value to the corresponding First Bank A/F values, as described above. Again, the offset value is determined based on the feedback signal received from the post-catalyst EGO sensor in the Second Bank. Then, the controller calculates a centroid value of the First Bank A/F waveform. Finally, the controller inverts the A/F values of the First Bank waveform about the centroid to generate an A/F waveform for the group of cylinders coupled to the Second Bank. As a result, the A/F waveform for the group of cylinders coupled to the Second Bank is inverted around the centroid relative to the A/F waveform for the group of cylinders coupled to the First Bank.
The disclosed methods and systems provide more responsive A/F values, and, as a result, permit the catalyst in the One-Sensor Bank to operate more efficiently compared to the known method of mirroring the A/F values in the two banks without using any feedback from the post-catalyst sensor in the One-Sensor bank.